A Small-Molecule Zwitterionic Electrolyte without a π-Delocalized Unit as a Charge-Injection Layer for High-Performance PLEDs

Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201 (China).
Angewandte Chemie International Edition (Impact Factor: 11.34). 03/2013; 52(12). DOI: 10.1002/anie.201209959
Source: PubMed

ABSTRACT Down to the bare bones: Small-molecule zwitterionic materials were found to be more efficient as charge-injection materials in an organic electronic device than a previously described polymer. Furthermore, the superior device performance observed for 1 indicates that it is not necessary to focus only on π-delocalized systems and that solid ionic liquids may be promising alternative candidates for charge-injection materials.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The power conversion efficiency (PCE) of bulk hetero-junction type polymer solar cells (PSCs) based on poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester can be enhanced by insertion of the thin layer of phenothiazine (PT)-based conjugated polymer electrolytes (CPEs), poly{10-[4-(N,N,N-trimethylammonium)butyl]-10H-phenothiazine} bromide (PHPT) and poly{10-butyl-10H-phenothiazine-alt-10-[4-(N,N,N-trimethylammonium)butyl]-10H-phenothiazine} bromide (PcoPT), at the cathode interface. The PHPT has quaternary ammonium salt on every side chains on PT rings whereas PcoPT has quaternary ammonium salt on the side chain on PT rings alternatively. Interestingly, regardless of high HOMO energy levels of PT-based CPEs (ca 5.0 eV), the thin layer of CPE at the cathode interface enhances the PCE by the formation of interface dipole which reduces the work function and a Schottky barrier at the cathode. It is also shown that the number of accumulated ionic groups of PcoPT on the photoactive active is larger than that of PHPT owing to the arrangement of side chain on the CPE backbone. In a similar way, the thin layer of PcoPT exhibits substantially better wetting ability on the photoactive layer than that of PHPT. Thus, the device with PcoPT exhibits higher short circuit current and fill factor than those of PSC with PHPT.
    Organic Electronics 11/2014; DOI:10.1016/j.orgel.2014.10.042 · 3.68 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Polyviologen (PV) derivatives are known as materials for adjusting the work function (WF) of cathodes, thereby reducing the electron injection/collection barrier at the cathode interface. In order to tune and improve the device performance, we introduce different types of counter anions (CAs), such as bromide, tetrafluoroborate, and tetraphenylborate in PV derivative. It is shown that the effective WF of the Al cathode depends on the size of CA, indicating that a Schottky barrier can be modulated by the size of CA. By increasing the size of CA from bromide to tetraphenylborate, the effective WF of the Al cathode is gradually decreased, indicating a decrease in a Schottky barrier at the cathode interfaces. In addition, the change of the power conversion efficiency (PCE) and the short circuit current (Jsc) value show good correlation with the change of the WF of the cathode, signifying the typical transition from a Schottky to an Ohmic contact. The turn on electric field of the electron only device without PV was 0.21 MV/cm, which is dramatically higher than the devices with PV-X (0.07 MV/cm for PV-Br, 0.06 MV/cm for PV-BF4, and 0.05 MV/cm for PV-BPh4). This is also coincident with a decrease in a Schottky barrier at the cathode interface. The device (ITO/PEDOT/P3HT:PCBM/PV/Al) with a thin layer of PV derivative with a CA of tetraphenylborate as a cathode buffer layer demonstrates the highest PCE of 4.02%, with an open circuit voltage of 0.64 V, a Jsc of 11.6 mA/cm2, and a fill factor of 53.0%. Here, our results show that it is possible to improve the performance of PSCs by choosing different types of CA in PV derivative without complicated synthesis and to refine the electron injection/collection barrier height at the cathode interface.
    ACS Applied Materials & Interfaces 01/2015; 7(5). DOI:10.1021/am5082606 · 5.90 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Disodium edetate (EDTA-Na), a popular hexadentate ligand in analytical chemistry, was successfully introduced in organic solar cells (OSCs) as cathode interfacial layer. The inverted OSCs with EDTA-Na showed superior performance both in power conversion efficiency and devices stability compared with conventional devices. Interestingly, we found that the performance of devices with EDTA-Na could be optimised through external bias treatment. After optimisation, the efficiency of inverted OSCs with device structure of ITO/EDTA-Na/polymer thieno[3,4-b]thiophene/benzodithiophene (PTB7):PC71BM/MoO3/Al was significantly increased to 8.33% from an initial value of 6.75%. This work introduces a new class of interlayer materials, small molecule electrolytes, for organic solar cells.
    ACS Applied Materials & Interfaces 11/2014; DOI:10.1021/am5044278 · 5.90 Impact Factor